Casting of polycarbonate dopes which contain a small amount of an alcohol



United States Patent 3,164,651 CASTWG F POLYCARBONATE DOPES WHICH CON TAIN A SMALL AMOUNT OF AN ALCOHOL James Chen-Fan Chu, Ridiey Park, Pa., assignor to General Aniiine & Film Corporation, New York, N.Y., a corporation of Delaware No Drawing. Filed Nov. 16, 1960, Ser. No. 69,569 4 Claims. (Cl. 264--216) The present invention pertains to casting polycarbonate resin to form a film and, more particularly, Itothe addition to the casing dope of an alcohol which serves to expedite the stripping of the cast film from the casting surface.

It is known that resins such as cellulose acetate, cellulose aceta-te butyrate and the like are cast on casting drums or bands provided with a casting surface of hydroacetate. The hydroacetate surface is produced by casting a solution of cellulose triacetate on the drum or band and hydrolyzing the triacetate to the desired depth. This procedure leads to a polished casting surface.

Polycarbonate resins are well known. They may be made, for example, by reacting diphenylcarbonate or phosgene with 2,2'-bis(4-hydroxyd-iphenyl)propane, generally known as bis-phenol A, or by reacting such bisphenol A with its bis-chloro carbonic acid ester. Polycarbonate resins, their preparation and certain solubility characteristics are described in Belgian Patents 562,543, 546,375, 546,376, 546,377, 553,614, 555,894, and 560,610; French Patents 1,152,155 and 1,152,156; German Patents 959,479 and 1,024,710; and U.S. Patent 2,799,666.

Polycarbonates, while possessing certain properties allied to polyethylene terephthalates, are distinguished, in part, by the fact that they may not only be extruded but, because of their solubility in certain solvents, may also be cast. Typically, the polycarbonates are soluble in such solvents as dioxane, ethylene dichloride, tetrachlorethane, benzene, toluene, chlorobenzene, trichloroethylene, chloroform and the like. It is therefore possible to provide casting dopes for the polycarbonates by dissolving the resin in one or a mixture of the above solvents.

Polycarbonate resins, however, due to their rather peculiar nature, are cast at a relatively slower speed than cellulose acetate or cellulose acetate butyrate under similar casting and curing conditions. At the usual low casting speeds, say, around 7 ft. per minute, the polycarbonate film tends to adhere to the hydrolyzed hydroacetate casting surface and when stripped therefrom causes snap bars at the strip off point. This-mitigates against the adoption of the casting method to produce sheets, films or foils of polycarbonate resins, particularly films designed for use as a base for light-sensitive silver halide emulsions. It is therefore necessary to improve the stripping characteristics of the polycarbonate film in order to promote the formation of a more uniform film and higher casting speeds.

It has now been discovered that the tendency of the polycarbonate to adhere to the hydrolyzed hydroacetate casting surface can be avoided if there be added to the casting dope a small quantity of a particular alcohol.

Casting dopes of polycarbonate resin so modified and the casting of polycarbonate from such dopes constitute the purposes and objects of the present invention.

The alcohols which I have found capable of removing the tendency of the resin film to adhere to the casting surused in equal parts by weight.

The quantities of the alcohol which are employed are very low compared to the over-all weight of the casting dope, amounting generally from about .02 to 1% by' r. CC

weight "thereof. Excellent results are obtained when operating with these small amounts of added alcohol.

The casting speed may vary from about 3 /2 to 20 ft. per minute, preferably 7 ft. per minute. Best results are found to accrue at the latter point.

The alcohol additions to the casting dope not only avoid formation of snap bars but, furthermore, noticeably reduce the stripping tension required. Thus, under identical casting conditions, the regular polymrbonate film, i'.e., without the alcohol addition, required amuch higher stripping tension than the modified polycarbonate. Finally, the alcohol additions were found to have no eflfgect on the otherwise excellent characteristics of the filmase.

The following examples will serve to illustrate the invention, it being understood that in these examples th dopes were cast on a casting band bearing a hydroacetate casting surface at a speed of about 7 ft. per minute.

Example I 20 grams of polycarbonate resin preferably produced by ester-interchange, i.e., reaction of diphenyl carbonate with -bis-phenol A, were dissolved in grams of methylene dichloride. To the resulting casting dope, there was added .125 gram of lauryl alcohol and the dope was cast to produce a film. The film was superior to that resulting from the casting of the resin from the methylene dichloride solution alone, exhibited no snap bars and was stripped at less tension than the resin cast from the methylene dichloride alone.

Example II Example I was repeated excepting that the quantity of lauryl alcohol was increased to .25 gram. A noticeable improvement over that of Example I was obtained.

Example III The procedure was the same as in Example I excepting that the quantityof lauryl alcohol was increased to .35 gram. A still further improvement resulted.

Example IV The procedure was the same as in Example I except- 7 ing that the quantity of lauryl alcohol was increased respectively to .5 and .75 gram. With these quantities, the results were found to be extremely good.

Example V The procedure was the same as in Example I excepting that the quantity of lauryl alcohol was increased to 1 gram. Excellent results were obtained but it was found that the film was slightly greasy, indicating that the top limit of alcohol addition had been approximately reached.

Example VI Four batches of a casting dope were prepared by dissolving for each batch 20 grams'of polycarbonate resin in 80 grams of methylene dichloride.

To the first batch there were added .025 gram of lauryl alcohol and .025 of myristyl alcohol.

To the second batch there were added .063 gram of lauryl alcohol and .063 gram of myristyl alcohol.

To the third batch there were added .125 gram of lauryl alcohol and .125 gram of myristyl alcohol.

To the fourth batch there were added .25 gram of lauryl alcohol and .25 gram of myristyl alcohol.

All of the batches were. cast at a speed of 7 ft. per minute on a hydrolyzed hydroacetate surface. It was found that the film from batch 4 was better than the film from the other three preceding batches, whereas the film from all of the batches excelled the film produced from adope containing no alcohol addition.

, 3 Example VII I The dope solution was prepared by dissolving 20 grams of polycarbonate resin in 80 grams of methylene dichloride, to which was added .5 gram of benzyl alcohol.

The film produced by casting this dope as in the :preceding examples was easily stripped from the casting surface and exhibited no snap bars.

In any of the above examples, the methylene dichloride solvent may be replaced by any other of the usual solvents for polycanbonates, such as dioxane, ethylene dichloride, benzene, toluene or the like.

Modifications of the invention will occur to persons skilled in the art. Ho'wever, it is to be understood that the invention is not restricted thereto.

1. The process of casting polycarbonate film While avoiding the occurrence of snap bar-s, which comprises casting on a hydrolyzed hydroacetate surface a stable casting dope consisting of polycarbonate resin, an organic solvent therefor and from about ,02 to 1% by weight of said casting dope of a small amount with respect to said organic solvent of an alcohol selected from the class consisting of lauryl alcohol, myristyl alcohol, benzyl alcohol and mixtures of lauryl alcohol and myristyl alcohol, drying to remove the solvent and stripping the film from the cast surface.

2. The process as defined in claim 1 wherein the dope is cast at a speed of 3 /2 to 20 feet per minute.

3. A casting dope capable upon stable casting of yielding film strippab-le from the casting surface without the creation of snap bars consisting of polycarbonate resin, an organic solvent therefor and from about .02 to 1% by Weight of the casting dope of an alcohol selected from the class consisting of lauryl alcohol, myristyl alcohol, benzyl alcohol and mixtures of lauryl alcohol and myristyl alcohol.

4. The casting dope as defined in claim 3 wherein the solvent is methylene dichloride and the alcohol is lauryl alcohol.

References Cited in the file of this patent UNETED STATES PATENTS 1,756,819 Ems et al. Apr. 29, 1930 2,874,046 Klockgether et al. Feb. 17, 1959 3,065,204 Dietrich et al. Nov. 20, 1962 FOREIGN PATENTS 578,585 Canada June 30, 1959 817,240 Great Britain July 29, 1959 OTHER REFERENCES Brit. Plastics, March 1958, pages 112-114. Christopher et al.: Polycarbonates; Reinhold Publishing Corporation, New York, 1962 (pp. 147-150) (Copy in Scientific Lib.) 

1. THE PROCESS OF CASTING POLYCARBONATE FILM WHILE AVOIDING THE OCCURENCE OF SNAP BARS, WHICH COMPRISES CASTING ON A HYDROLYZED HYDROACETATE SURFACE A STABLE CASTING DOPE CONSISTING OF POLYCARBONATE RESIN, AN ORGANIC SOLVENT THEREFOR AND FROM ABOUT .02 TO 1% BY WEIGHT OF SAID CASTING DOPE OF A SMALL AMOUNT WITH RESPECT TO SAID ORGANIC SOLVENT OF AN ALCOHOL SELECTED FROM THE CLASS CONSISTING OF LAURYL ALCOHOL, MYRISTYL ALCOHOL, BENZYL ALCOHOL AND MIXTURES OF LAURYL ALCOHOL AND MYRISTYL ALCOHOL, DRYING TO REMOVE THE SOLVENT AND STRIPPING THE FILM FROM THE CAST SURFACE. 